One of the main problems which occurs in hydraulic engineering is the corrosion of metals in both treated and untreated cooling water systems. The corrosion of metals such as steel, aluminum, brass and copper which are commonly found in water systems, is primarily due to dissolved oxygen and carbon dioxide. Materials which remove oxygen such as sodium sulfite or hydrazine are not economical and are technically inadequate. Hence Zn.sup.++, chromates, molybdates, polyphosphates, ortho-phosphate, and organo-phosphonates are added to cooling water to form protective films on metal surfaces. Chromates are very efficient corrosion inhibitors. However, they are often environmentally undesirable due to the well known toxic effects. Zn.sup.++ has similar environmental problems and it also has low solubility products with ortho phosphates, hydroxide and carbonate which can form sludge and deposits responsible for promoting corrosion. Polyphosphates are not as efficient as chromates and they are unstable in a cooling water environment, thus they decompose by hydrolysis to ortho and pyro-phosphates which often cause sludge and deposits. Ortho-phosphates are not as efficient as chromates and if they are not controlled properly they can also form sludge and deposits. Although organo-phosphonates provide some corrosion protection, they are not nearly as efficient as chromates.